Surface morphologies of SnO2(1 1 0)

Scanning tunneling microscopy (STM), ion scattering spectroscopy (ISS), and low energy electron diffraction (LEED) was used to investigate the surface morphology of SnO2(1 1 0) for different preparation conditions. Annealing in 10−3 mbar oxygen results in a 1 × 1 diffraction pattern. Such surfaces exhibit terraces separated predominantly by straight step edges along low index crystallographic directions. The terraces exhibit a high density of defects. Annealing to 810 K results in the loss of surface oxygen but the surface retains a 1 × 1 periodicity. Steps of less than monolayer-height, however, indicate that a significant reordering of the surface atoms occurs already at this temperature. Annealing to higher temperature or preparation of the surface by sputtering and vacuum annealing always results in a superstructure in the diffraction pattern and a low [O]/[Sn] ratio in ISS. For annealing temperatures between 920 and 1050 K co-existence of c(2 × 2) and 4 × 1 reconstructed domains is observed. In this regime small adislands are always present at the surface; extended terraces were imaged by STM with a 4 × 1 periodicity. This implies that the c(2 × 2)-structure is associated with adislands at the surface. Annealing to 1100 K resulted in the formation of a 4 × 1 surface only. This surface exhibits terraces with meandering step edges and antiphase domain boundaries of the 4 × 1 surface structure. A new model for this reconstruction is proposed including Sn atoms occupying interstitial surface sites. Annealing to 1180 K results in the fragmentation of the 4 × 1 structure and the surface looses its long-range order. This causes a 1 × 1 LEED pattern originating from the underlying substrate. Surface undulations with sub-interlayer step heights are explained by the frequent presence of stacking faults and other bulk defects that are also accompanied by variations in the electronic structure due to a locally altered Sn/O stoichiometry.